JPS6256191A - Photo-recording medium - Google Patents

Abstract

PURPOSE:To enable signals to be recorded and read out without the use of a reflection layer composed of an inorganic compound by a method in which a photo-recording layer is made up of a transparent base plate and a recording layer containing a specific naphthalocyanic dye, and the thickness of the recording layer is controlled. CONSTITUTION:A photo-recording medium is made up of a transparent resin base plate and a recording layer containing a naphthalocyanic dye of the formula (I), where R1, R2, R3, and R4 are each a 4-12C straight chain or branched chain alky incidently or differently, R5, R6, R7, and R8 are each a 1-12C straight or branched chain alkyl incidently or differently, k, l, m, and n are each 0 or 1 but not zero at the same time, and M is a metal or its oxide or halogen compound. The thickness of the recording layer is 50-400mum. Since the recording layer has sufficient reflectivity, signals can be written or read out without the use of a reflection layer composed of inorganic compounds, and great S/N ratio can be obtained. The photo-recording medium has high stability against heat and moisture.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to an optical recording medium that can be additionally recorded using a focused beam of a semiconductor laser, and more specifically relates to a computer external memory, various types of information such as images, audio, etc. The present invention relates to an optical recording medium used for recording.

[Prior art]

As the above-mentioned write-once optical recording medium, recording media having an inorganic recording layer made of a thin film of a low-melting metal such as tellurium, tellurium alloy, bismuth alloy, etc. are beginning to be put into practical use. However, these recording media have low productivity because they require the formation of a recording layer in a vacuum such as vacuum evaporation or sputtering, and the recording density and recording sensitivity are low because the recording layer has a high thermal conductivity. However, since it uses toxic substances such as tellurium, there are particular concerns about its toxicity when it is used for civilian purposes.

In order to solve these problems, in recent years optical recording media with organic dye films as recording layers have been studied. For example, dithiol metal complexes (US Pat. No. 4,465,767,
9.826), polymethine dye (JP-A-58-112)
No. 790), squalium dye (Japanese Patent Application Laid-open No. 58-1127
No. 92), naphthoquinone dye (JP-A-58-I1279)
No. 3), phthalocyanine dye (U.S. Patent No. 4298.97)
No. 5), naphthalocyanine dye (U.S. Pat. No. 4.492.
An optical recording medium having a recording layer made of an organic dye that absorbs at the oscillation wavelength of a semiconductor laser, such as No. 750), has been proposed. However, the media that used organic dyes in the recording layer, which had been proposed in the past, (a) lacked durability;
b) Because the reflectance of the recording layer is low, a separate reflective layer made of an inorganic compound such as a thin metal film or a thin metal oxide film is required; Ta.

This (a) lack of durability is due to the fact that the characteristics of the media change over time, so special consideration must be taken when storing the media, and if the same track is read repeatedly, the read I7 The medium may be affected by the light and the information may not be read correctly.

This change due to the readout light can be avoided by reducing the output of the readout light, but in this case, the light intensity is small, so noise is picked up and the signal-to-noise ratio (S
/N) becomes small, it is difficult to cause the laser to emit light stably at low output, and the load on the readout circuit increases, which is undesirable. Furthermore, (b) the need to separately provide a reflective layer made of an inorganic compound due to the low reflectance not only complicates the manufacturing process of the optical recording medium but also is expected due to the low thermal conductivity. There is a problem in that the high recording density and recording sensitivity of organic dye-based recording films are reduced or canceled out by using an inorganic compound with high thermal conductivity as a reflective layer. Furthermore, (c) the poor solubility of organic dyes makes it impossible to use the coating method, which is the most productive method for forming a recording layer.
Even if a recording layer could be formed by a coating method, it was not possible to directly coat the soil of a thermoplastic resin substrate, which does not have excellent solvent resistance, because the solvents that can be used are limited. When a thermoplastic resin substrate is used, the dye liquid is applied through a resin having excellent solvent resistance such as an ultraviolet curable resin, which makes the process complicated and is not desirable from the viewpoint of productivity and economy.

[Basic idea]

The inventors of the present invention have conducted intensive studies to improve the above-mentioned drawbacks of optical recording media with an organic dye film as a recording layer. By controlling the film thickness to an appropriate thickness, it not only has durability that could not be achieved with conventional optical recording media using organic dyes, but also because the recording layer itself has the function of a reflective layer. They discovered that it is possible to form an optical recording medium that does not require a separate reflective layer made of an inorganic compound, and thus completed the present invention.

[Disclosure of the invention]

That is, the present invention provides an optical recording medium for recording and reproducing signals using reflected light, which includes a transparent resin substrate and the following general formula (1) (where R + R2 + R3 and R4 have a carbon number of 4 to 12
represents a straight chain or branched alkyl group, R5, R6
R7 and R8 represent a straight chain or branched alkyl group having 1 to 12 carbon atoms, and these groups may be the same or different. k, 1. m.

n represents 0 or 1, and f, m, , n cannot all be O at the same time (i.e. k + 1 + m + n and 1)
. It may be. M represents a metal and a metal oxide or halide. To provide an optical recording medium comprising a recording layer having a film thickness of 50 to 400 nm containing a naphthalocyanine dye shown in .

In the present invention, it is preferable to write and read signals using a light beam that passes through a transparent substrate, since this makes it less susceptible to dust, scratches, and the like. Therefore,
The transparent resin substrate used in the present invention preferably has a light transmittance of 85% or more for writing and reading signals, and has small optical anisotropy. For example, thermoplastic resins such as acrylic resins, polycarbonate resins, polyester resins, polyamide resins, vinyl chloride resins, polyvinyl ester resins, polystyrene resins, polyolefin resins (poly-4-methylpentene, etc.), polyethersulfone resins, and epoxy resins, Examples include substrates using thermosetting resins such as allyl resins. Among these, the above-mentioned thermoplastic resins are preferred from the viewpoint of ease of molding and ease of providing guide grooves, address signals, etc., and acrylic resins and polycarbonate resins are particularly preferred from the viewpoint of optical properties and mechanical properties.

In the present invention, the thickness of these transparent resin substrates is not particularly limited, and may be plate-like or film-like. Further, the shape may be circular or card-like, and there is no particular restriction on the size.

In addition, these transparent resin substrates of the present invention usually have guide grooves for position control during recording and reading, and unevenness for preformatting such as address signals and various marks. It is preferable to apply it using a stun bar or the like when molding (injection, compression, etc.) the thermoplastic resin as described above.

In the present invention, on such a substrate, the following general formula (1) (wherein R + R2 + R3 and R1 have 4 to 1 carbon atoms)
Represents two straight-chain or branched alkyl groups, R5゜R
, Rヮ and R8 represent a straight chain or branched alkyl group having 1 to 12 carbon atoms, and these groups may be the same or different. K,! .

m and n represent 0 or 1, and J-, m, n
do not all become 0 at the same time (i.e. k +j! +
m-1-n! 1). M represents a metal and a metal oxide or halide. ) A recording layer containing a naphthalocyanine dye shown in the following is provided.

R□ in the naphthalocyanine dye represented by the general formula (1) used in the recording layer in the present invention.

Specific examples of the alkyl substituent represented by R2+ R3 and R4 include n-butyl,! SOS boolean, 5ec
-butyl, tert-butyl, n-amyl, lSOS boule, 5eC-amyl, tert-amyl, n-hexyl, 1so-hexyl, 1-methyl-1-ethylglobil, 1,1-dimethylbutyl, n-heptyl, tert
Examples include heftyl, octyl, 2-ethylhexyl, nonyl, decyl, dodecyl, and the like.

These alkyl substituents may be bonded to either the 6-position or the 7-position of the naphthalene nucleus of the naphthalocyanine/naphthalocyanide, or may be a mixture thereof. On the other hand, R5゜R6, R7 and R8 of the naphthalocyanine dye represented by the general formula (1)
As a specific side of the alkyl substituent represented by R□+
R2+ Those listed as specific examples of the alkyl substituent represented by R3 and R6, as well as methyl, ethyl, n
-propyl, 1so-propyl, and the like. On the other hand, in the above general formula (1), the expression f787=2 dyes and filters. One example is CuXNi, MgXPd, V,
Co, Ti, Nb.

At, Sn, In, Fe, Or XGe, Mn
, Mo, Ga, Tt.

Oa, Sr, Ba, pb, sb,
Examples include metals such as Ta, and oxides, chlorides, bromides, and iodides of these metals. These metals, metal oxides, chlorides, bromides, or iodides are usually
However, it may be a mixture of monovalent and hexavalent. R in the naphthalocyanine dye of general formula (1), R2゜R
If the number of carbon atoms in the alkyl substituents represented by 3 and R4 is 3 or less, it is difficult to fix (form) a recording layer by coating, which is the easiest method, because of poor solubility in common solvents such as benzene and toluene. This is not desirable. From the viewpoint of solubility in this solvent, those in which the number of carbon atoms in these alkyl substituents is 5 or more are more preferable. On the other hand, when the number of carbon atoms exceeds 12, the reflectance of the recording layer containing it becomes low, which is not preferable. Also, in terms of reflectance and absorbance, M in the naphthalocyanine dye is Cu.

Ni, Mg, pd Xpb, Co, Nb
XNb0, Sn, In.

Ge, Ga, TtVO (vanadyl), ht-a
t, Fe-Ct.

Particularly preferred is TaO.

These dyes may be used alone or in combination of two or more.

The naphthalocyanine dye used in the present invention is
Zh, Obs, Khim, 42696-699 (19
It can be easily synthesized according to the known method described in 72) et al.

In order to fix (form) the recording layer on the transparent resin substrate in the optical recording medium of the present invention, for example, a naphthalocyanine dye can be fixed by methods such as vacuum evaporation, sputtering, and ion blasting. Since this method requires complicated operations and is inferior in terms of productivity, a so-called coating method is most preferred.

To fix the recording layer by coating, a dye solution consisting of the naphthalocyanine dye and an organic solvent described above is brought into contact with the substrate to fix the dye onto the substrate. A method in which the liquid is allowed to flow down or the surface of the substrate is brought into contact with the liquid level of the dye liquid and then pulled up and the excess liquid is removed while rotating the substrate;
There is a method in which the dye liquid is caused to flow down onto the substrate while rotating the substrate. If necessary, forced drying may be performed after this. The organic solvent used at this time may be a usual solvent that dissolves naphthalocyanine dyes, such as pentane, n-hexane, isohexane, 6-methyl-pentane, neohexane, 2,3-dimethylbutane, n-hexane, 2. -Methylhexane, 3-methylhexane, 3
-ethylpentane, 2.2-dimethylpentane, 2.3
-dimethylpentane, 2.4-dimethylpentane, 3.
3-dimethylpentane, 2,2,5-trimethylbutane, n-octane, isooctane and other isomers of octane, nonane and its isomers, decane and its isomers.
Saturated aliphatic hydrocarbons such as undecane and dodecane; pentene, hexene and its isomers, hexadiene and its isomers, hexatriene, heptene and its isomers, heptadiene and its isomers, hepta) IJene, octene and its isomers , octadiene, octatriene,
Unsaturated aliphatic hydrocarbons such as nonene, nonadiene, nonatriene, diyne, undecene, dodecene; cyclopentane, methylcyclopentane, dimethylcyclopentane, ethylcyclopentane, cyclohexane, methylcyclohexane, dimethylcyclohexane, ethylcyclohexane, isopropylcyclohexane, cyclo Saturated alicyclic hydrocarbons such as heptane; cyclopentene, cyclopentadiene, cyclohexene, methylcyclohexene,
Unsaturated alicyclic hydrocarbons such as dimethylcyclohexene, ethylcyclohexene, cyclohexadiene, methylcyclohexadiene, and cycloheptene; and terpene hydrocarbons such as diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, diimbutyl ether, dipentyl ether, etc. Aromatic hydrocarbons such as benzene, toluene, xylene, and ethylbenzene; Ester solvents such as ethyl acetate, butyl acetate, amyl acetate, and ethylene glycol monoethyl ether acetate; acetone, methyl ethyl ketone, and methyl isobutyl ketone Ketone solvents such as , cyclohexanone, and isophorone; Alcohol solvents such as ethyl alcohol, furoyl alcohol, butyl alcohol, amyl alcohol, ethylene glycol monomethyl ether, ethylene glycol monomethyl ether, and benzyl alcohol; Chloroform, carbon tetrachloride, methylene chloride, Halogenated hydrocarbons such as methyl chloroform, tricrene, tetrachlorethylene, dichloroethylene, dichloroethane, and tetrachloroethane; cyclic ethers and diglyme such as tetrahydrofuran and dioxane;
Examples include dimethylformamide.

As described above in the present invention, it is preferable to use a thermoplastic resin such as acrylic resin or polycarbonate resin as the resin substrate and apply the dye liquid directly to the thermoplastic resin substrate. The surface of the substrate may be damaged by the dye liquid, and from the viewpoint of damage to the resin substrate, as we have already proposed, it is recommended that the solubility parameter be 8 among the above-mentioned solvents that dissolve the dye. Solvents with a molecular weight of .6 or less are more preferred. What is the solubility parameter in this case (where δ: solubility parameter, ΔHv: heat of vaporization, V
”: represents molar volume), and Δ
HV is calculated from the boiling point according to the Hildebrand rule: ΔHv29B = 23.7Tb + 0.0
The value is 20Tb''-2950 (Tb: boiling point). Therefore, the solubility parameter is also a value of 298°.For details regarding these calculation methods, please refer to J. H. Hilde.
brand, '5olu-bility of
Nonelactrolytes'424-427 (1
950) Reinhold Publisher+g
Co., Ltd. The solvents of the present invention may be used alone or in combination of two or more. The solubility parameter when two or more types are mixed is the sum of the products of the volume fraction of each mixed solvent and the solubility parameter of each solvent, that is, the value determined by the following equation.

δ=Vxδ1+■2δ2+■3δ3+-・-+Vnδn
Vl, V2, V3,..., Vn: Volume fraction δl, δ2 of each solvent in the mixed solvent. δ3. ..., δn: Solubility parameter of each solvent in the mixed solvent ~ The concentration of the dye liquid in the present invention varies depending on the type of solvent and coating method, but is usually 0.1 to 10% by weight, preferably 1 to 0. .5 to 5% by weight. At this time, a soluble resin such as nitrocellulose, ethyl cellulose, or acrylic resin, or additives such as a leveling agent and an antifoaming agent may be added to the dye liquid as a binder for the dye. However, adding too much resin component or additive tends to cause a decrease in the reflectance of the recording layer, and the amount added is 20% relative to the dye.
It is preferably at most 10% by weight, more preferably at most 10% by weight.

Further, other dyes may be mixed with the dye liquid for use. Pigments that can be used in combination (7) are already known such as aromatic or unsaturated aliphatic diamine metal complexes, aromatic or unsaturated aliphatic dithiol metal complexes, phthalocyanine complexes, alkylnaphthalocyanine complexes,
Examples include squalium dyes, naphthoquinone complexes, anthraquinone dyes, and polymethine dyes. When adding these dyes, it is necessary to select a solvent so as to dissolve both these dyes and the dye of the present invention, and also to avoid a significant decrease in the reflectance of the recording layer. From the viewpoint of reducing reflectance, it is preferable to select polymethine dyes and naphthoquinone complexes.

In the optical recording medium of the present invention, as described above, it is preferable to record and reproduce signals using a light beam passing through a transparent substrate (a light beam irradiated from the substrate side). In such cases, if the thickness of the recording layer becomes too thick, the writing light will be absorbed and attenuated considerably as it passes through the thick recording layer, and the recording layer surface (the surface in contact with air) will be attenuated considerably. does not fully reach. Therefore, the amount of light on this surface is insufficient and the temperature rise is insufficient, making it impossible to satisfactorily form unevenness corresponding to the signal.

As a result, the sensitivity decreases, and even if recording is possible, the 8/N (signal-to-noise ratio) value when reading out the signal is too small to be of practical use.

On the other hand, if the thickness of the recording layer is too thin, as will be described later, a sufficient reflectance in the recording layer cannot be obtained due to light interference, and therefore a large S/N value cannot be obtained.

Therefore, it is necessary to form a recording layer with an appropriate thickness, and the thickness of the recording layer in the optical recording medium of the present invention is preferably 50 to 350 nm, more preferably 60 to 180 nm. .

There are various methods for measuring film thickness, and it is quite difficult to obtain accurate measured values, but it is preferable to use values measured using an ellipsometer. Note that it is particularly difficult to measure the film thickness when there are guide grooves on the substrate, but the film thickness when the dye is fixed on the same substrate without unevenness such as guide grooves can be used as a substitute.

The most characteristic feature of the present invention is that the recording layer formed in this way has a fairly high reflectance, and therefore the recording layer itself also functions as a reflective layer. It is something that we have at the same time.

Therefore, the optical recording medium of the present invention is capable of controlling the focus of a laser beam when recording or reading signals without providing any reflective layer made of an inorganic compound such as a metal thin film, metal oxide, or metal alloy thin film as in the past. This makes it possible to control the writing position of signals.

To write a signal in the optical recording medium of the present invention, a laser beam is irradiated with a focused laser beam on the recording layer. The dye in the recording layer in the irradiated area absorbs the laser beam and generates heat, which changes the quality of the recording layer, forming irregularities and reducing the reflectance, thereby allowing writing to be performed. Signals are read by detecting this change in reflectance using a finer laser beam, but generally, if the change in reflectance is small, the signal-to-noise ratio (S/N') is undesirable.

In order to obtain a large S/N value, the original reflectance through the substrate before a signal is written is at least 10% or more, preferably 15% or more. This 10%
A reflectance of preferably 15% or more can be easily achieved by using the dye of the present invention and by appropriately selecting the thickness of the recording layer. However, the reflectance changes depending on the film thickness due to interference of reflected light from the front and back sides of the recording layer.

For example, Figure 1 shows the results of our measurements of the relationship between film thickness and reflectance when tetra-6-t, crt-amyl-tetra-7-methyl-2,6-naphthalocyanine vanadyl was used in the recording layer. show. The reflectance measurement in this case is 800
Using a light source with a wavelength of ±50 nm, the recording layer is fixed on a transparent substrate with no unevenness such as guide grooves, and measurement is performed through the transparent substrate using a spectrophotometer equipped with a 5° specular reflection accessory. However, the reflectance in the present invention means the value measured in this manner.

In putting the optical recording medium of the present invention into practical use, the S/N
In order to improve the value, an anti-reflection layer is provided, an ultraviolet curing resin is coated on the recording layer to protect it, a protective sheet is pasted on the recording layer surface, and the recording layer surfaces are placed on the inside. Known means such as laminating two sheets together may also be used. It is preferable to provide an air gap on the recording layer when laminating the recording layers together.

The present invention will be explained in more detail below using Examples.

Example 1゜(1) Thickness: 1.2mm, diameter: 130mm, spiral guide groove (depth: 70nrn, width: 0.6μm, pitch: 1.6μm)
Tetra-,5-tert-amyl-tetra-7-methyl-
2,6-naphthalocyanine vanadyl color! After dropping a solution consisting of 1.2/N parts and 8 parts by weight of carbon tetrachloride,
The substrate was rotated at a speed of 1000 rpm for 10 seconds. Next, this substrate was dried in an atmosphere of 40° C. for 10 minutes to fix the recording layer to the acrylic resin substrate. Note that the thickness of the recording layer measured on the flat surface of the guide groove was 110 nm using an ellipsometer. Also, the reflectance of light with a wavelength of 850 nm through the acrylic resin substrate is 2.
It was 0%.

(2) Place the optical recording medium thus produced on a turntable with the recording layer facing up, and while rotating at a speed of 900 rprn, equip a semiconductor laser with an oscillation wavelength of 830 nm and an output of 13 mW at the substrate surface. Using this optical head, a 1 MHz pulse signal was recorded while controlling the laser beam to be focused on the recording layer from below the optical recording medium through the acrylic resin substrate. Next, using the same equipment, the output of the semiconductor laser was adjusted to O1 on the substrate surface.
The recorded signal was reproduced in the same manner at 7 mW.

The signal-to-noise ratio (S/N) at this time was 50 decibels, and very good signal writing and reading could be performed.

(3) 60'C to check the durability of this optical recording medium.
After leaving it in an atmosphere of 19 SIU for 4 months, signals were recorded on the unrecorded part using the same method as above, and the recorded signal before the durability test and the recorded signal after the durability test were played back. s of 48.49 decibels, respectively.
/N was obtained, and the change due to the durability test was sufficiently small.

(4)'lj: Oh, I observed the shape of the bit in the signal recording section after the durability test using a scanning electron microscope, and the bits recorded before and after the durability test were almost the same. In optical recording media with such a shape and an inorganic thin film such as p-based or Te-based inorganic thin film as a recording layer, there is almost no bulging at the edge of the bit, which is thought to occur due to the high thermal conductivity and causes noise. The bit shape was very nice.

Example 2. Comparative Example 1 Carbon tetrachloride of a naphthalocyanine dye having M and the substituents shown in Table 1 instead of the tetra-6-tert-amyl-tetra-7-methyl-2,3-naphthalocyanine vanadyl dye in Example 1 An optical recording medium was prepared using the solution in the same manner as in Example 1, and the film thickness, reflectance, and S/Nt- were determined by a recording and reproducing test.

The results are summarized in Table 1.

Example 3 A polycarbonate resin substrate having guide grooves having the same shape as in Example 1 and a 3-weight-hair octane solution of tetra-6-octyl-7-ethyl-2,3-naphthalocyanine vanadyl dye were prepared as in Example 1. An optical recording medium was made in the same way. The thickness of the recording layer on a flat surface that does not interfere with the guide groove is 90 nm.

The reflectance of light at 8300 m through the polycarbonate resin substrate was 17%. Further, recording characteristics and durability were evaluated in the same manner as in Example 1. The S/N is 52 dB'''C immediately after recording, and even when played back again after the durability test, the 8/N is 51 dB, and even when recorded and played back again after the durability test, the S/N is 51 dB, so there is almost no deterioration. When the shapes of the bits were observed, it was found that there was a bulge on the edge of each bit both immediately after recording and after the durability test, and no change was observed even after the durability test.

〔Effect of the invention〕

As described above, in the optical recording medium of the present invention, the recording layer itself has a sufficient reflectance, so even if a reflective layer such as a metal thin film or a metal oxide thin film is not provided, the signal can be transmitted. It is possible to perform reading and reading, and since the reflectance is large, the size Z
O/N ratio can be obtained. V The optical recording medium of the present invention is stable against heat and humidity and can be used for a long period of time.

Furthermore, the fact that the shape of the bit in the recording section does not show any ridges on the edges confirms that S/N can be obtained, and at the same time, the possibility of an increase in recording density is recognized. .

[Brief explanation of the drawing]

FIG. 1 is a graph showing an example of the relationship between reflectance and film thickness of the recording layer of the present invention. Here, an example is shown in which tetra-(5-tert-amyl-tetra-7-methyl-.2,5-naphthalocyanine vanadyl) is used as the naphthalocyanine dye.

Claims (2)

[Claims] (1) Transparent substrate and the following general formula provided on the substrate (1) ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (1) (In the formula, R_1, R_2, R_3 and R_4 have 4 to 4 carbon atoms.
Represents 12 straight chain or branched alkyl groups, R_5
, R_6, R_7 and R_8 represent a straight chain or branched alkyl group having 1 to 12 carbon atoms, and these groups may be the same or different at the same time. k, l, m, n
represents 0 or 1, and k, l, m, and n are not all 0 at the same time (that is, k+l+m+n≧1). M represents a metal and a metal oxide or halide. )
50-30 containing the naphthalocyanine dye shown in
An optical recording medium consisting of a recording layer having a film thickness of 0 nm and capable of recording and reading signals without having a reflective layer made of an inorganic compound. (2) The optical recording medium according to claim 1, wherein signals are recorded and read by a light beam passing through a transparent substrate.